When do octane levels matter?

[SiI40sx]

Ok well basically my friend is very ignorant and I wanted to explain to him how octane levels dont really matter, especially on a stock car. I told him that octane levels are only needed on highly boosted cars due to the lower octanes not keeping up with the combustions and causing bad combustions in the motor. How can I explain to him what octane levels mean? I kind of need this as backup as he is a very hard headed bitch! So yea I need proof! Go you! Zilvian techies!

[dct223]

your definition of octane is mixed up...

higher octane gas does not combust as easily as lower octane...

[marshun]

www.google.com

www.hotstuffworks.com

yay

[SiI40sx]

www.google.com

www.hotstuffworks.com

yay

i think u mean HOWstuffworks buddy, not your pr0n links

[nrg]

octane is needed to keep control of detonation and knocks.
http://www.oregon.gov/ODA/MSD/docs/pdf/gas_octane_guide.pdf
http://science.howstuffworks.com/gasoline3.htm

[NemeGuero]

i think u mean HOWstuffworks buddy, not your pr0n links

LMAO.. fuckin' pwned

[SochBAT]

I dnno about you, but regardless of stock or not, octane matters to me. If i want a good running, better mile-getting engine, i'd always rock higher octane.

To my knowledge, the higher the octane levels, the easier, and more efficient it is to combust, and cleaner it burns, with lower carbon monoxide. I forget, but im lazy to research it. And i guess octane booster just contains a more concentrated volume of octane, so it makes your current fuel a little more rich.

Now, to search...

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From HowStuffWorks...

The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites. When gas ignites by compression rather than because of the spark from the spark plug, it causes knocking in the engine. Knocking can damage an engine, so it is not something you want to have happening. Lower-octane gas (like "regular" 87-octane gasoline) can handle the least amount of compression before igniting.

The compression ratio of your engine determines the octane rating of the gas you must use in the car. One way to increase the horsepower of an engine of a given displacement is to increase its compression ratio. So a "high-performance engine" has a higher compression ratio and requires higher-octane fuel. The advantage of a high compression ratio is that it gives your engine a higher horsepower rating for a given engine weight -- that is what makes the engine "high performance." The disadvantage is that the gasoline for your engine costs more.

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The higher the octane level, the lower your chances of knock.

[dct223]

good search but you need to change your statement "the higher the octane levels, the easier, and more efficient it is to combust,"

read the 1st paragraph from how stuff works again...

[Kn1ves]

in regards to our cars, i got about a 3mpg difference between a 87 and 91

test was done twice on each octane

87 averaging 27mpg (26.832 and 27.332)

and 91 averaging 30mpg (29.995 and 30.175)

this was done with a 230 mile trip back and forth from los angeles to san diego at around 2am in the morning each time holding a steady, and i mean STEADY 65mph (left at 2:10, and at 3:09 odometer said 64 miles and turned to 65 at exactly 3:10)

everytime i take a trip, i fill up before i leave

car has new fuel filter, spark plugs, and o2 sensor
car has 149,081 miles right now

interesting facts ::
car gets 24mpg~ if i mix city/highway 65-80mph
car gets 20mpg~ if i drive avg of 100mph (not safe i know but its 2am in the morning)

i still continue my trips to SD every other friday or so... and hold a steady 65mph with my foot (no cruise) just to save $$ it costs me about $10 one way to SD about 3 gallons of gas

[Kn1ves]

i forgot to mention, this is with the stock KA24DE with minor modifications to intake. it has a home depot ram air with stock air box and paper filter. theres a 90degree smooth bend pipe with a funnel at the end behind the left turn signal. it connects perfectly to the stock y pipe that connects to the air box as well. if anyone wants to see the pics i can upload, but its not that interesting

[mrmephistopheles]

My .02USD:
I took two cross-country trips in '03 (1 roundtrip from San Diego to Jacksonville, NC), and took copious notes (which I currently can't find) regarding my fuel economy.
At all times, my car got the cheapest gasoline possible, 86-88 octane, depending upon where I was in the country.

My average for the trip was 29.1mpg, and I cruised at 85mph for the great majority of the trip. The best economy I got was 31mpg, again at ~85mph the whole duration. It felt REALLY good to get over 400 miles to a tank of gas.


in regards to our cars, i got about a 3mpg difference between a 87 and 91

test was done twice on each octane

87 averaging 27mpg (26.832 and 27.332)

and 91 averaging 30mpg (29.995 and 30.175)

this was done with a 230 mile trip back and forth from los angeles to san diego at around 2am in the morning each time holding a steady, and i mean STEADY 65mph (left at 2:10, and at 3:09 odometer said 64 miles and turned to 65 at exactly 3:10)

everytime i take a trip, i fill up before i leave

car has new fuel filter, spark plugs, and o2 sensor
car has 149,081 miles right now

interesting facts ::
car gets 24mpg~ if i mix city/highway 65-80mph
car gets 20mpg~ if i drive avg of 100mph (not safe i know but its 2am in the morning)

i still continue my trips to SD every other friday or so... and hold a steady 65mph with my foot (no cruise) just to save $$ it costs me about $10 one way to SD about 3 gallons of gas

[SiI40sx]

so according to this thread, higher octane levels do make a difference in performance? and even in mpg?

[nrg]

didn't mythbuster do the gas octane thing? and it was false.
alot of things can change the way you gain miles per gallons. your throttle, the ammount of gas you really have (stock gauge isn't accurate)

performance wise only depends on how the motor is made to use the octane. It's not a magic potion.

[SiI40sx]

man theres no such thing as 91! Its all 87, the rest are just damn placebo's!

[HalveBlue]

This myth was busted on Mythbusters as well as Dateline (or one of those shows).

Higher Octane levels prevent premature detonation. They do not enhance fuel economy. Because fuels ignite under certain amounts of pressure higher octane fuels are designed to withstand a greater amount of pressure before ignition. This is the reason FI engines need higher octane fuels to run effectively and efficiently.

Also, I think most cars are designed to be most fuel effecient between 55-65 mph. Or at least that was the theory behind instituting the 55 mph speed limit on interstate highways during the oil crisis in the 70s.

[Flybert]

The only time that higher octane is needed is when your car detonates and knocks. I use my SAFC2 to monitor knock on my SR and it works really well.

[SiI40sx]

Thats what I thought, basically in the posts stated above of howstuffworks.com, octane(8) is basically the number carbon chains it contains and according to research, 8 chains of carbon dont ignite as easily as the rest while being put under pressure (when the cylinder compresses to tdc) and basically the higher the octane level the harder it is for the octane to ignite under pressure. So there is no reason to put higher octane levels in a stock car?

[seanc]

you guys are only taking into one variable combustion pressure. nissan ecu's use a knock sensor to monitor, you guessed it knock. if the sensor see's no knock it will keep the timing advanced and allow you a better burn more complete burn of the a/f during the combustion process resulting in better emissions and better mpg. higher octane resists knock more than lower octane hence the reason why it is used in cars that are running more boost and ignition timing.

[McRussellPants]

higher octane just makes sure its the spark causing ingnition, not a hot spot making a random flame front.

Any high HP/L car should run the highest octane availible.

[jonny_290]

seanc nailed it, it improves performance because it lets your ECU run more aggressive timing

[theicecreamdan]

octane is a measurement of how long it takes for the fuel to burn. Low octane fuel burns quickly and easily. High octane takes longer to burn.

using a higher octane fuel in a car that doesn't need it is pointless. Using lower octane fuel in a car that needs the high octane will cause excessive wear on the engine and could lead to premature failure.

[2_fast_240]

I think it helps performance on a stock 240. Why else would it say "for maximum performance run premium fuel" in the owners manual.